This application is based upon and is entitled to the benefit of priority from the prior Japanese Patent Application No. 2001-116268, filed Apr. 16, 2001, the entire contents of which are incorporated herein by reference.
This invention relates to a manufacturing method of an optical fiber cable, and more specifically relates to a manufacturing method of an optical fiber cable having a plurality of optical fiber.
An optical fiber cable is generally formed by binding up a plurality of optical fibers. Each optical fiber is coated with a jacket of a different color so as to visually differentiate each fiber easily. When eight optical fibers are to be bound, for example, jackets of white, blue, yellow, green, red, purple, brown, and orange are used. Also, jackets are sometimes identified by their patterns.
Conventionally, each optical fiber is coated with a jacket appropriate color at wire drawing. To manufacture a long haul optical fiber cable, a predetermined number of optical fibers respectively coated with a jacket of different color are bound up while optical fibers with a jacket of same color are fused in an axial direction.
In the conventional method, differences of transmission characteristics, for example, chromatic dispersion, of a plurality of optical fibers in one cable are considerable. Accordingly, it is difficult to match the transmission characteristics of each optical fiber. For example, when a dispersion compensating fiber is inserted to compensate accumulated chromatic dispersion in a cable, it is necessary to select a dispersion compensating amount, namely a length of dispersion compensating fiber one by one for every fiber. This operation becomes a severe burden.
Conventionally, to unify transmission characteristics of optical fibers in a cable, the transmission characteristics are previously measured to select optical fibers having similar characteristics and then an optical cable is manufactured using the selected fibers alone. However, in this method, a yield becomes quite low. That is, although a small number of optical fiber cables having unified characteristics are obtained, a large amount of material is merely wasted.
In accordance with the present invention, a method to manufacture an optical fiber cable containing n (n is an integer no less than 2) optical fibers is provided. In an initial step mutually different unique identifiers are added to the n optical fibers in a first span. In an identifier adding step the identifiers are added in order obtained when the n optical fibers in the first span are arranged according to a predetermined characteristic value to n optical fibers in a second span one by one wherein the n optical fibers in the second span are arranged in inverse order to that of the first span according to the predetermined characteristic value. In a connecting step the n optical fibers in the first span are connected to those in second span so that each optical fiber having the same identifier are coupled together. In a repeating step such operation is repeated until a desired span number that the identifiers in order obtained when the antecedently connected n optical fibers are arranged according to the predetermined characteristic value are added to n optical fibers in the following span one by one, wherein the n optical fibers in the following span are arranged in inverse order to that of a previous span according to the predetermined characteristic value and that the antecedently connected n optical fibers and those of the following span connect each other so that each optical fiber having a same identifier are coupled together.
With the above configuration, differences of predetermined characteristic values between optical fibers become smaller as the number of spans increases because the optical fibers are added so as to reduce the differences of the predetermined characteristic values between the optical fibers. It is not to select nor use optical fibers having a desired characteristic value alone but to use manufactured optical fibers in a wide range, and accordingly a high yield is achieved.
An identifier is a color and/or pattern of jacket to coat each optical fiber. A predetermined characteristic value is, for example, chromatic dispersion.